Table 1. Bias assessment and study data.
NIH Bias Assessment Tool was used [12]
NR: Not Recorded, Y: Yes, N: No, NIH: National Institutes of Health
1. Research question with the goal 2. Defining study populations clearly 3. Sample size justification 4. Groups recruited from the same population 5. Specify and apply inclusion and exclusion criteria 6. Defined description of cases and controls 7. Random sampling 8. Concurrent controls used 9. Exposure assessed prior to the outcome measurement 10. Details of exposure measures 11. Blindness of exposure assessors 12. Adjustment for confounding variables
| Study | Case total (N) | Control total (N) | Sample | Bias | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| Chagury et al., 2018 [14] | 34 | 594 | Brazilian | fair | Y | Y | NR | N | Y | Y | Y | N | NR | Y | NR | Y |
| Fang et al., 2017 [15] | 105 | 420 | Chinese Hans | good | Y | Y | NR | Y | Y | Y | Y | Y | NR | Y | NR | Y |
| Esmaili et al., 2013 [16] | 50 | 180 | Iranian | fair | Y | Y | NR | N | Y | Y | Y | Y | NR | Y | NR | Y |
| Schwarm et al., 2021 [17] | 446 | 433 | German | fair | Y | Y | NR | Y | Y | Y | NR | N | NR | Y | NR | NR |
| Ujie et al., 2018 [18] | 72 | 873 | Japanese | good | Y | Y | Y | Y | Y | Y | Y | NR | Y | Y | NR | Y |